Optical sensor particulate classification using optical response signal analysis

Abstract

A system comprises a particle sensor for a vehicle comprising a light source that directs a beam to an interrogation region outside the vehicle; and an optical detector that receives scattered or reflected light from an aerosol particle in the interrogation region. A processor performs a method for particle classification comprising measuring an optical response from a single particle in the interrogation region by identifying an optical response peak for scattered or reflected light from the interrogation region; measuring an amplitude and duration of the optical response peak; correcting the duration of the optical response peak based on a vehicle airspeed; based on the measured amplitude of the optical response peak, generating an expected optical response duration for water droplet using a calibration table; analyzing the measured optical response duration and the expected optical response duration to determine particle classification; and generating classification probabilities for one or more particle types.

What is claimed is: 
     
         1 . A system comprising:
 a particle sensor assembly for a vehicle, the particle sensor assembly comprising:
 a light source configured to direct a light beam to an interrogation region outside of the vehicle; and 
 an optical detector configured to receive scattered or reflected light from an aerosol particle in the interrogation region; and 
   a processor in operative communication with the optical detector;   wherein the processor hosts a module that includes program instructions, executable by the processor, to perform a method for particle classification comprising:
 measuring an optical response from a single particle in the interrogation region by a process comprising:
 identifying an optical response peak for scattered or reflected light from the interrogation region; 
 measuring an amplitude and duration of the optical response peak; and 
 correcting the duration of the optical response peak based on an airspeed of the vehicle; 
 
 based on the measured amplitude of the optical response peak, generating an expected optical response duration for a water droplet using a calibration table; 
 analyzing the measured optical response duration and the expected optical response duration to determine a particle classification; and 
 generating classification probabilities for one or more particle types. 
   
     
     
         2 . The system of  claim 1 , wherein the particle classification comprises water droplets, ice crystals, volcanic ash, sand, or dust. 
     
     
         3 . The system of  claim 1 , wherein the particle classification of the single particle is determined by a process comprising:
 calculating a difference value between the measured duration of the optical response peak and an expected optical response peak duration; and   comparing the difference value to a predefined difference threshold to determine the particle classification.   
     
     
         4 . The system of  claim 3 , wherein:
 if the difference value is less than the predefined difference threshold, then the single particle comprises a water droplet;   if the difference value is greater than the predefined difference threshold, then the single particle comprises an aspherical particle.   
     
     
         5 . The system of  claim 4 , wherein:
 the optical response peak is resampled based on the airspeed of the vehicle;   based on the measured amplitude of the optical response peak, an expected optical response peak shape for a water droplet is generated using the calibration table; and   a shape of the resampled optical response peak is compared with the expected optical response peak shape.   
     
     
         6 . The system of  claim 5 , wherein:
 other identified peak parameters are used to enhance particle type classification accuracy, including a peak curve being present within a 1-sigma/2-sigma/X-sigma limit of expected water droplet optical response, or analyzing a peak symmetry.   
     
     
         7 . The system of  claim 1 , wherein the system:
 collects optical response data from multiple measurements of individual particles; and   determines a particle classification by statistical analysis of optical response peak duration and optical response peak amplitude data.   
     
     
         8 . The system of  claim 7 , wherein:
 a two-dimensional histogram is generated, where a first axis describes optical response peak amplitude, and a second axis describes optical response peak duration; and   a variance of optical response peak duration for each histogram column of optical response peak amplitude is calculated.   
     
     
         9 . The system of  claim 8 , wherein:
 if a difference between an expected variance for water droplets and calculated values of variance is below a defined threshold, then the particles comprise water droplets;   if the difference between an expected variance for water droplets and calculated values of variance is above the defined threshold, then the particles comprise aspherical particles.   
     
     
         10 . The system of  claim 8 , wherein:
 the variance of each histogram column is compared with expected variance values for water droplets, ice crystals, and volcanic ash/sand/dust particles; and   based on a difference of measured variance and the expected variance for each particle type, the system generates a probability for each type of particle, and determines a most probable type of particle.   
     
     
         11 . The system of  claim 8 , wherein the processor uses the optical response peak duration and the optical response peak amplitude of the two-dimensional histogram as an input into a computer model, including an expert system, a probabilistic model, or a machine learning system, wherein the computer model is operative to determine a most probable particle type. 
     
     
         12 . The system of  claim 8 , wherein:
 the processor generates features describing a two-dimensional data distribution of optical response peak duration and optical response peak amplitude, and propagates these features into a computer model, which also takes as an input other features, including depolarization signal parameters;   wherein the computer model uses all existing input features to determine a most probable particle type.   
     
     
         13 . A method comprising:
 transmitting a light beam from a light source on a vehicle, to an interrogation region outside of the vehicle;   receiving, in an optical detector on the vehicle, scattered or reflected light from an aerosol particle in the interrogation region outside of the vehicle;   measuring an optical response from the aerosol particle in the interrogation region by identifying an optical response peak of the scattered or reflected light from the interrogation region, and resampling the optical response peak based on a value of an airspeed of the vehicle;   measuring an amplitude, duration and shape of the resampled optical response peak;   based on the measured amplitude of the optical response peak, generating an expected optical response for a water droplet using a calibration table, and the duration and shape of the optical response peak;   analyzing the measured optical response and the expected optical response to determine a particle classification of the aerosol particle; and   generating a probability value for a particle type of the aerosol particle.   
     
     
         14 . The method of  claim 13 , wherein the particle classification of the aerosol particle is determined by a process comprising:
 calculating a difference value between the measured duration of the optical response peak and an expected optical response peak duration; and   comparing the difference value to a predefined difference threshold to determine the particle classification.   
     
     
         15 . The method of  claim 14 , wherein:
 if the difference value is less than the predefined difference threshold, then the aerosol particle comprises a water droplet;   if the difference value is greater than the predefined difference threshold, then the aerosol particle comprises an aspherical particle.   
     
     
         16 . The method of  claim 15 , wherein:
 other identified peak parameters are used to enhance particle type classification accuracy, including a peak curve being present within a 1-sigma/2-sigma/X-sigma limit of expected water droplet optical response, or analyzing a peak symmetry.   
     
     
         17 . The method of  claim 13 , further comprising:
 collecting optical response data from multiple measurements of individual particles; and   determining a particle classification by statistical analysis of optical response peak duration and optical response peak amplitude data.   
     
     
         18 . The method of  claim 17 , further comprising:
 generating a two-dimensional histogram, where a first axis describes optical response peak amplitude, and a second axis describes optical response peak duration; and   calculating a variance of optical response peak duration for each histogram column of optical response peak amplitude.   
     
     
         19 . The method of  claim 18 , wherein:
 if a difference between an expected variance for water droplets and the calculated variance is below a defined threshold, then the particles comprise water droplets;   if the difference between an expected variance for water droplets and the calculated variance is above the defined threshold, then the particles comprise aspherical particles.   
     
     
         20 . The method of  claim 18 , wherein:
 the variance of each histogram column is compared with expected variance values for water droplets, ice crystals, and volcanic ash/sand/dust particles; and   based on a difference of measured variance and the expected variance for each particle type, generating a probability for each type of particle, and determining a most probable type of particle.